Ester-containing lubricant compositions



2,898,299 ESTER-CQNTAHJING LUBRICANT COMPQSITIONS Warren Lowe, Berkeley, Calif., assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Application May 31, 1957 Serial No. 662,580 6 Claims. (Cl. 252'46.6)

The present invention relates to new and useful compositions of matter and pertains more particularly to novel compositions containing a major proportion of an oil of lubricating viscosity. This application is a continuation-in-part of my earlier copending application Serial No. 416,428, filed March 15, 1954, now abandoned,

which in turn was a continuation of my applications esters of partially dehydrated aliphatic polyhydric alco-' hol such as sorbitan monostearate are added to sloshing oils to prevent rusting or to prevent corrosive attack on steel by sulfur dioxide and water vapor; esters of saccharoses such as pentastearyl glycose are proposed as wax suppressors for waxy lubricating oils, etc.

With the refinements now being made in automotive and other internal combustion engines, a great deal of attention is being directed to the provision of a lubricant which will permit the engine to be operated at a'high level of efficiency over long periods of time. The primary function of the lubricant is, of course, to reduce friction and thereby not only decrease the wear on pistons, piston walls, bearings and other moving parts, but also increase the efficiency of the engine. It is also a function of the lubricant to prevent the deposition of solid products on the piston walls and other surfaces of the engine coming in contact with the lubricant. Such deposits seriously interfere with eflicient engine operation for they accelerate piston ring and cylinder wall wear and also increase oil losses by plugging the oil ring grooves. The troublesome deposits which form on the face of the piston and on the other walls of the combustion chamber, as well as on valves and spark' plugs are also partially attributable in many cases to the lubricant. It is of importance to eliminate or at least minimize the formation of all such deposits, and it is the basic object of this invention to achieve such a result.

T o a minor degree, certain of the deposits formed on engine surfaces have their origin in the oil itself, that is to say, in the decomposition products of the oil. A more important, though still minor, source of engine deposits lies in the additives with which oils are conventionally supplied. This is particularly the case with metal- 2 Accordingly, it is a particular object of this invention to provide a lubricant composition which is compounded with metalor mineral-free detergents and wear-reducing additives.

While certain of the additives heretofore employed in oils (and to a lesser degree the oil itself) are partially responsible for deposits which form on engine surfaces, it is now recognized that the major source of such deposits or their precursors lies in the various aldehydes, acids, oxy-acids and other similarly reactive, partiallyoxidized combustion products of the fuel. These prodnets are formed both under pre-ignition conditions as well as during the combustion step proper, particularly during the period before the engine has reached operating temperature. Accordingly, under city driving conditions where the engine is repeatedly started in the cold condition and is seldom driven for a distance sufficient containing additives as, for example, the organic, metal- 7 to reach the most efficient operating temperatures, the formation of partial oxidation products is particularly severe. carried down into the crankcase of the engine along with other blow-by gases, and since most are insoluble or only sparingly soluble in lubricating oils, they tend to separate from the oil and adhere to engine surfaces or form large droplets. In either case, under the elevated temperature conditions prevailing in the engine, these reactive monomers quickly polymerize to form solid masses which readily deposit out on the engine wall surfaces.

It is the practice in the art to prevent the formation of such deposits by adding to the lubricant a material normally referred to as a detergent. Insofar as is known, all the detergent additives which have heretofore been successfully employed on a commercial scale are organic, metal-containing compounds such as calcium petroleum sulfonate, calcium cetyl phosphate, calcium octyl salicylate, calcium phenyl stearate, the barium salt of wax-substituted benzene sulfonate, or the potassium salt of the reaction product of phosphorus pentasulfide and polybutene. Various of these detergents 'act by reacting chemically with deposit precursors to form harmless compounds. Others act to prevent flocculation or coagulation of solid particles in the oil and maintain the same in a state of suspension as finely divided particles. It has been found that detergents can be designed not only to perform this dispersant function but also to effect the solubilization or emulsification of the sparingly soluble monomers in the oil and thereby greatly reduce the rate of polymerization. In the latter case, such polymer materials as do then form within the body of the oil are smaller in size and can be peptized or dispersed in the oil much more readily than is the case with the larger polymeric particles which are formed on exposed engine surfaces or in droplets lying without the oil.

Detergents capable of acting in the latter fashion are preferably employed wherever possible, particularly in automotive engines to be operated under city driving conditions. For this purpose certain esters of higher polyhydric alcohols have been found to be quite effective. The detergent action of the polyhydric alcohol esters appears to depend on unesterified free hydroxyl groups since, for example, in the series of pentaerythritol esters, the detergent action increases as the degree of esterifi'cation decreases. Similarly detergent efficiency is increased in going from sorbitan trioleate to sorbitan monooleate. At least one esterifying acid radical is required to impart sufficient oil-solubility to the molecule.

The effectiveness of these partial esters to prevent engine deposits is illustrated by the results shown in the following table of FL2 Chevrolet engine tests of crankcase lubricants containing various esters as the sole compounding agent. Given for comparison are tests on the Many of these partial oxidation products are Piston Rating Test No. Additive Nnne Commercial type compounding 10% Pentaerythritol tetraoleate- 10% Pentaerythritol dioleate" 10% Pentaerythritol monooleat 5% Pentaerytliritol monooleate 10% Sorbitan monooleate 10% Sorbitan trioleate..- 10% Glyceryl monooleate s s ss ss w oczosnkqcemmo Compounding:

None (base oil alone, average of several runs) 10% pentaerythritol monooleate 10% pentaerythritol monooleate +0.1% qnimzarim 10% pentaerythritol monooleate +01% 10% pentaerythritol monooleate mm 10% pentaerythritol monooleate +1% suliurized olefin inhib 10% pentaerythritol monooleate +1% sulfurized di-paraltin wax sulfide- 10% pentaerythritol monooleate +1% dilauryl selem'de 10% pentaerythritol monooleate +1% phenyl alpha naphthylamine 10% pentaerythritol monooleate phenothiazinm pentaerythritol monooleate +1% 2,2-methylene bis(4-methy1 10% pentaerythritol monooleate +05% p-hydroxy diphenylamine.-- 10% pentaerythritol monooleate +2% zine dibutyl dithiocarbamate 10% pentaerythritol monooleate +1% aromatic amine inhibitor B 10% pentaerythritol monooleate +1% 2,6 di-tertiary-butyl 4-methyl phenoL- 10% pentaerythritol monooleate +2% plume-P285 condensation product 10% sorbitan monooleate 10% sorbitan monooleate +2% pinene-PzS5 reaction product 10% sorbitan monooleate +0.15% cateehol 10% glyceryl monooleate 10% glyceryl monooleate +2% pinene-Pzss reaction product 10% glyceryl monooleate +2% sullurized olefin inhibitor A Other partial esters as described below will give similar results.

While these partial esters impart satisfactory detergency to oils and do not appear to have any adverse effects when employed under quite mild service conditions, we have found that the free hydroxyl groups in the partial esters act at elevated temperatures to promote corrosion of sensitive bearing metals such as copperlead, cadmiumsilver, cadmium-nickel, the so-called high lead bearing alloys, and the like. These sensitive bearing metals are susceptible to attack by acidic and/ or peroxidic materials; this phenomenon has been designated as acid or oxidation corrosion." To illustrate the corrosivity at elevated temperature, oil compositions containing the partial esters were subjected to a strip corrosion test which indicates the relative corrosivity at actual engine operating conditions. The results of the -hour 300 F. corrosion test (subsequently described in more detail) are given in the following table:

Compounding: Table H Weight loss (mgs.)

None (base oil alone, average of several runs) 38 5% pentaerythritol monooleate 60.4 10% pentaerythritol monooleate 66.0

5% pentaerythritol dioleate 117.1

5% pentaerythritol tetraoleate 40.1 5% monoester of pentaerythritol and soya bean oil fatty acids 64.6 5% inositol pentanaphthenate 71.1 5% pentaerythritol dinaphthenate 67.3 5% pentaerythritol monostearate 97.2 5% sorbitan monostearate 120.0 5% sorbitan trinaphthenate 169.0 5% sorbitan tristearate 124.0 5% sorbitan monooleate 77.4 10% sorbitan monooleate 142.4 5% sorbitan trioleate 61.8 10% glyceryl monooleate 59.3

alizarin ./kg. zinc dicetyl-phenyl dithiophosphate- The above tests illustrate the corrosivity imparted to the base oils by the addition of the partial esters.

Surprisingly, it was found that the corrosion promoting effect of the partial esters is uniquely diificult to counteract. In fact, it was discovered that various agents effective to decrease the oxidation corrosion of usual lubricating oil compositions are not appreciably effective in oils containing partial ester detergents. In other words, agents which might be called conventional corrosion inhibitors are not appreciably effective in oils containing partial esters. Actually, in many cases this so-called corrosion inhibitor further increases the corrosion rather than behaving as an inhibitor. This unexpected phenomenon is illustrated in the following table of results obtained by subjecting oil compositions containing the corrosive partial esters plus various conventional inhibitors to the strip corrosion test.

Table III rtor A Of the various agents employed in the test reported in the foregoing table, the sulfuriz/ed olefin inhibitor A is a product marketed by Enjay Company, Inc., under the trademark Paranox 12. The sulfun'zed diparaifin wax sulfide was prepared substantially in accordance with Example 1 of Clausen and Rutherford Patent 2,514,625. The aromatic amine inhibitor B is a product marketed by E. I. du Pont de Nemours & Company, Inc., under the trademark Ortholeum 300. The pinene-P S reaction product was prepared in accordance with May Patent 2,486,188 and contained approximately 3.35% phosphorus and 8.71% sulfur.

In light of the foregoing negative results with the addition of various agents to the corrosive partial estercontaining oils, it was particularly unexpected to discover that the oxidation corrosion attack on hard bearing metals such as copper-lead alloys at elevated temperatures by these corrosive partial ester-containing oils could be greatly reduced, to the desired minimum, by the combination of certain vicinal dihydroxy aryl compounds with oil-soluble reaction products of olefins and sulfur or phosphorus sulfide. The effect of this combination is particularly surprising since neither one alone has a marked effect on the corrosion of the ester-containing oils. The combination of agents is synergistic in the compositions of the present invention.

The inhibitor combination will find ready use not only in those partial ester-containing oils which are extremely corrosive but also in such oils which are mildly corrosive. Not only the elevated temperatures to which such oils are subjected but also other factors such as improvements in the mechanical arts come into play and contribute to the seriousness and importance of the oxidation corrosion problem and the need for a counteractant. Thus, modern internal combustion engines and other mechanisms employing oil of lubricating viscosity are so carefully designed and built and the clearances so small that they cannot tolerate even relatively mildly corrosive oils which were satisfactorily used in the past. Because of these low tolerances the inhibition of mildly corrosive oils by means of our agents can be the most important aspect of the present invention, and such inhibition will be, under some circumstances, the more diflicult problem to overcome in the absence of our agents. That is, reducing the corrosivity to the extremely low minimum is often more difiicult than just reducing the corrosivity from extremely corrosivefto mildly cortests for various oil compositions containing partial esters with and without the agents of the present inhibitor combination, the same base oil being used throughout the test.

Table IV Weight loss Compounding: (mgs;)

N o compounding (base oil alone, average of several runs) 38 10% sorbitan mono 142. 4 10% sorbitan monooleate +2% pinene-P fi 133. 2 10% sorbitan monooleate +2% pinene-PzS +0.15% al lzar m 1. 8 10% sorbitan monooleate +1% pinene-PzSz, +0.15% alrzar m 12. 9 10% sorbitan monooleate +2% pinene-PZS5 +0.10% alrzarrn- 27. 5 10% sorbitan monooleate +2% sulfurized terpene inhibitor +0.15% alrzarin 0.7 10% sorbitan monooleate +2% sulfurized olefin inhibitor A +0.15% al1zar1 .n 10. 2

10% sorbitan monooleate +2% sulfurized mixed olefin polymer +0.15% alrzarrn +13 10% sorbitan monooleate +0.15% catechol 96 10% sorbitau monooleate +2% pinene-IzSr. +0.15% catech 2. 6 10% sorbitan monooleate +2% pinene-PrSa +0.10% 14. 7 10% sorbitan monooleate +2% pinene-PZSE +0.05% catecbol 25. sorbitan monooleate +2% pinenePzSr +0.15% pyrn allnl 1s, 5

10% sorbitan monooleate +2% sulfurized mixed olefin polymer +0.15% catechol +30 5% sorbitan trioleate 61. 8 5% sorbitan trioleate +2% pinene-Pzss +0.15% alizarn1 23. 3 5% sorbitan trioleate +2% pinene-P2S +0.15% catech 16. 4 5% pentaerythritol monostear re 97. 2 5% pentaerythritol monostearate +2% pinene-PrSs catechol- 24.1

5% sorbitan mon0stearate 120 5% sorbitan monostearate +27 pinene-PzSa +0.15% catech 3. 8 10% glyceryl monooleate 82. 4 10% glyceryl monooleate 2% pinene-PzS +0.15% catcch l7. 4

rosive. By extremely corrosive oils is meant those oils characterized by a corrosivity of greater than about 40 mgs. Weight loss of a 2 /2-inch by 1 inch by 1 inch section of a copper-lead bearing insert in a -hour 300 F. corrosion test (subsequently described in more detail). A mildly corrosive oil is characterized by a bearing weight loss in the same test of from 20 to mgs. The foregoing 40 mgs. and 20 mgs. bearing weight losses can be designated as corrosion indices of 40 and 20 respectively.

To illustrate the corrosion-inhibitory properties of the inhibitor combination in the new oil compositions of the present invention, a section of a copper-lead bearing insert having the dimensions of about 2 /2 inches by ;inch by 1 inch was first cleaned with a wire brush until :the strip was highly polished. The strip was weighed and the wei ht recorded. The highly polished strip was :completely immersed in the test oil. The oil was stirred ;at a temperature of 300 F. for 2.0 hours, at which time .the strip was removed and cleaned, first with chloroiorm, and then with petroleum ether. The strip was then weighed and the difference in weight of the original strip :and the strip after the solvent wash was noted and re- .corded as the weight loss due to corrosion by the oil .composition.

Oils which are noncorrosive as shown by this test are admirably suited for use as inhibited electrical insulating oils, cable oils, etc. Also, oils passing this test, and when otherwise satisfactory, can be employed for other purposes. Thus, for example, the oils containing the partial esters in sufficient'amount to impart detergency, i.e., to decrease engine deposits satis- Compounding:

10% sorbitan monooleate 10% sorbitan monooleate +2% pinene-PzSs reaction product- 10% sorbitan rnonooleate +2% pinene-PzSs reaction product +0.15% quinizarin 10% sorbrtan monooleate +2% pinene-P2S5 reaction product +0.15% 1,8-dihydroxy raq 10% sorbrtan monooleate +2% BURKE-P255 reaction product +0.15% para-tertiary butyl catecho In the foregoing table the commercial sulfurized terpene inhibitor C is a product marketed by E. I. du Pont de Nemours & Company, Inc. under the trademark Ortholeum 202. The sulfurized mixed olefin polymer was prepared by heating a mixture of about 200 parts of heavy propylene polymer (average molecular weight: approximately 180), 200 parts of butylene polymer (average molecular weight=about 530), 25 parts of QR oleic acid and parts of C.P. flowers of sulfur, to a temperature of 375-3 F. for 2 hours, hydrogen sulfide being evolved during the reaction; during the heating and cooling down nitrogen was bubbled through the mixture; clay was added when the temperature reached F.; the reaction mixture was filtered through a clay cake at 90 F., yielding a product of clear dark red-brown color and having an average molecular weight of 395, a gravity of 22.4 A.P.I. at 60 F., a bromine number of 50, and 13.0% sulfur. Other partial esters as described below will give similar results.

The above results illustrate that the addition of the inhibitor combination of the present invention in every case clearly lowered the oxidation corrosion, whereas in contrast thereto the addition'of the organic sulfur inhibitor alone was relatively ineffective.

When the vicinal polyhydroxy aryl compounds are replaced with polyhydroxy aryl compounds in which the hydroxy groups are not on adjacent carbon atoms of the benzene ring, an adverse eifect results. Thus, as shown in the following table, the substitution of quinizarin for alizarin, 1,3-dihydroxy benzene for catechol-(l,2-dihydroxybenzene), and like substitutions bring about an increase in the corrosivity of the oil compositions.

Table V 10% sorbitan monooleate +2% pinene-PgSs reaction product +0.15% bis-1,4-(2,3-dihydroxy-ph di methylbutane 1 89. 8 10% sorbitan monooleate +2% pinene-Pzss reaction product +0.15% 1,3dihydroxy benzene 118. 7 10% sorb tan monooleate +2% prnene-PzSs reaction product +0.15% 1,4-dihydroxy benzene-- 213. 9 10% sorbrtan monooleate +2% plnenc-PzSt reaction product +0.15% 1,3,5-trihydroxy benzene 190. 6 10% sorbrtan monooleate +2% Dinette-P255 reaction product +0.15% 1,5-dil1ydroxynaphthalen 116. 5

e 10% sorbitan monooleate +2% pinene-PZSE reaction product +0.15% 2,6-di-tertiary butyl 4-m thyl phenoL 10% sorbitan monooleate +2% pinene-PzSa reaction product +0.15% naphthol- .I. 1

It will be seen from the data of the foregoing Table V that the combinations of the sulfur-containing inhibitor with non-vicinal polyhydroxy benzene compounds are not effective to reduce the oxidation corrosivity of oil compositions containing partial esters. Thus, the effective inhibitor combinations are those in which the benzene compounds have at least two hydroxyl groups on adjacent carbon atoms of the ring (see Table IV). It will be further noted from Table V that bis-l,4(2,3-dihydroxyphenyl)-2,3-dimethylbutane in the combination gives borderline results but that increasing the ratio of aliphatic carbons in alkyl substituents to aromatic carbons, as with paratertiary butyl catechol, brings about an adverse effect.

Thus, the vicinal polyhydroxy aryl compounds in the inhibitor combination of the present normally-corrosive partial ester-containing oils can be defined as polyhydroxy benzenes and anthraquinones having at least two hydroxy groups on adjacent carbon atoms of a benzene ring. The vicinal polyhydroxy benzenes are exemplified by catechol (1,2-dihydroxybenzene), pyrogallol (1,2,3- trihydroxybenzene), 1,2,4-benzenetriol (1,2,4-trihydroxybenzene), apionol (l,2,3,4-tetrahydroxybenzene), etc. The benzene ring can be substituted with methyl groups or other short chain alkyl groups or two benzene rings can be linked together with short alkylene groups. In such substituted dihydroxybenzenes, there should be no more than half as many aliphatic carbon atoms as aromatic. Preferably there should be besides the hydroxyl groups no more ring substituents than two alkyl groups of no more than three carbon atoms. Ordinarily the unsubstituted vicinal polyhydroxybenzenes are preferred.

The vicinal dihydroxyanthraquinones are exemplified by alizarin (l,Z-dihydroxyanthraquinone), hystazarin (2,S-dihydroxyanthraquinone), etc. and various substituted derivatives thereof including those containing additional hydroxy groups such as in alizarin RG (1,2,7- trihydroxyanthraquinone), alizarin SG (1,2,9-trihydroxyanthraquinone), anthragallol (1,2,3-t1'ihydroxyanthraquinone), quinalizarin (1,2,5,8-tetrahydroxyanthaquinone), alizarin garnet (l,2-dihydroxy-4-amino-anthraquinone), etc. The vicinal dihydroxy anthraquinones may be substituted with one or two short chain alkyl groups such as methyl, propyl, etc. but not such which by their structure and/or position substantially decrease the reactivity of the vicinal hydroxy groups by stearic hindrance or resonance. Ordinarily it is preferred to use the unsubstituted vicinal dihydroxyanthraquinoues.

The other component of the inhibitor combination is a reaction product of an olefin with elemental sulfur or preferably a phosphorus sulfide such as P S The olefin is of sufficient chain length (usually of at least 8 carbon atoms) and character to impart enough oleophilic properties to make the reaction product oil-soluble to the extent desired for incorporation in the final oil composition. Suitable sulfurized olefins include sulfurized ethylene-propylene copolymers, sulfurized polybutenes, sulfurized terpenes such as Du Ponts Ortholeum 202, and the like. The reaction products of terpenes and phosphorus sulfides are described, for example, in May Patent 2,486,188.

The foregoing combination of agents of this invention are not limited to their applicability to any particular base stock which contains an ester. The advantages herein disclosed can be obtained with various corrosive estercontaining oils of the lubricating class, the selection of which will be determined by conditions and services which the compounded oil is to encounter. Ordinarily the oil alone will not be appreciably corrosive, and of concern here is the substantial increase in corrosivity brought about by the addition of the partial esters. The compounding ingredients are useful not only in Pennsylvania oils or highly refined naphthenic oils, but also in moderately-refined naphthenic base oils or in lubricating oils from Mid-Continent stocks, as well as in synthetic hydrocarbon oils such as hydrogenated polymers of olefin hydrocarbons or synthetic non-hydrocarbon oils of lubrieating viscosity such as condensation products of chlorinated alkyl hydrocarbons with aryl compounds, polyether oils, etc. Suitable polyether synthetic oils are obtained by the polymerization of lower molecular weight (e.g., C to C alkylene oxides, such as propylene and/or ethylene oxides, and derivatives and mixtures thereof to liquid products of lubricating oil viscosity; included in the term polyether oils are the derivatives obtained by etherification and/or esterification of the hydroxy groups in the alkylene oxide polymer, such as for example, the acetate of the 2-ethyl hexanol initiated polymer of propylene oxide. Various polyether oils are described in Patents 2,425,755; 2,448,664; 2,480,185; 2,520,614; and others.

Synthetic oils of the dicarboxylic acid ester type include those which are prepared by esterifying such dicarboxylic acids as adipic acid, azelaic acid, suberic acid, sebacic acid, alkenyl succinic acid, fumaric acid, malcic acid, etc., with alcohols such as butyl alcohol, hexyl alcohol, 2-ethylhexyl alcohol, dodecyl alcohol, etc. Examples of such ester oils are dibutyl adipate, dihexyl adipate, di-2-ethylhexyl sebacate, etc.

The esters in the oil compositions in which my inhibitor combination is incorporated are the higher polyhydric aliphatic alcohols partially esterified with an aliphatic carboxylic acid having an oil-solubilizing chain of at least 8 carbon atoms. Since as indicated above the effectiveness of the esters to inhibit deposit formation in engines depends at least in part upon unesterified hydroxyl groups, it is preferred that at least two, and most desirably all but one, of the hydroxyl groups remain unesterified. For appreciable effectiveness as a detergent additive, the alcohol should contain at least three, preferably four or five, and including six hydroxyl groups. Suitable alcohols which may be employed in forming the esters are exemplified by glycerol, tetrahydric alcohols such as erythritol, pentaerythritol, etc., the pentahydric alcohols such as penitol, tetramethylol cyclohexanol, etc., hexahydric alcohols such as sorbitol, mannitol, inositol, etc., ether alcohols including polyglycols such as diethylene glycol, polypentaerythritols such as dipentaerythritol, etc., anhydro alcohols such as sorbitan, mannitan, etc., derivatives of anhydro alcohols such as the polyoxyalkylene derivatives of sorbitan and mannitan, and the like. For some uses, the tetraor higher poly-hydric alcohols are preferred. When the esters are employed primarily to prevent rusting, as in an aircraft engine preservative oil, the inhibitor combination therewith is required to counteract the corrosive attack on sensitive bearing metals at the elevated temperatures encountered when the engine is operated.

Representative higher aliphatic carboxylic acids which can be employed to form the above-described esters include capric, undecylic, lauric, myristic, palmitic, stearic, arachidic, behenic, and melissic as well as the higher naphthenic acids and naphthenic acid mixtures of the type derived from petroleum. Also, mixtures of acids derived from natural sources such as coconut oil, lard oil, tallow, cottonseed oil, soyabean oil and palm oil can be used. Among the higher aliphatic acids, a preferred group comprises those containing 10 or more carbon atoms and a single olefinic carbon-to-carbon double bond, as exemplified by 9-undecylenic, 4-tetradecylenic, oleic, palmitoleic, ricinoleic, elaidic and brassidic acids.

While the acids and alcohols employed in forming the esters of the present invention have been referred to as aliphatic in character, such term is also intended to include acids of the type defined above which are substituted by one or more of various groups such as amino, hydroxyl, alkoxy, chloro, phenyl, and the like, particularly when the number, nature and position of such substituent groups is not sufficient to alter the essentially aliphatic character and stability under the se- 9 lected conditions of use of the ester. The term also includes higher cyclic aliphatic acids and alcohols as exemplified, respectively, by the naphthenic acids and sorbitan.

Of the various partial esters indicated above, the monooleates of pentaerythritol and sorbitan are preferred for their outstanding effectiveness as detergents.

The esters of the above-disclosed alcohols and acids will ordinarily be present in the base oil in amounts ranging from about 2 or 3% to 10 or 15%, although in some cases they can be present in amounts as small as 0.5 to 1%. Generally not more than 25% of the esters will be incorporated in the oil compositions. Ordinarily the partial esters, 'When used to impart detergency characteristics to a crankcase lubricant, will be employed in amounts ranging preferably from about to about of the final lubricant composition. While some esters appear to have limited solubilities in very light mineral oils, they are readily soluble up to 12 to 20% or more in oils normally used as lubricants. Usually the esters can be dispersed in amount greater than their apparent solubility limits.

The inhibitor combination is incorporated into the ester-containing oil in suflicient amount to inhibit substantially against corrosion attack on hard bearing metals. In general, the amount of organic sulfide inhibitor required in the combination for substantial reduction of the corrosion ranges from about 0.05% up to 5% or more by weight of the finished oil; preferably the organic sulfide inhibitor is kept at a minimum below 3.0% but above 0.1%. The vicinal polyhydroxybenzenes are eliective for the present purpose when used in amounts as low as about 0.005%, but are ordinarily employed in amounts ranging from 0.03% up to about 1.5%, depending on the limits of solubility, although amounts greater than 0.5% are not usually required. The higher amounts of the inhibitor usually will be required for crankcase lubricants for internal combustion engines. The minimum amount of the sulfur inhibitor for this purpose ordinarily will be 1%. The lower proportions of the inhibitor combination will be satisfactory where the conditions of use of the compounded oil are less rigorous, though at elevated temperature, than encountered in internal combustion engines. Thus, where the desired life of the oil or the temperature is not as high as in an internal combustion engine, the combination of the inhibitors at the lower percentages will be effective and satisfactory. In any event, an efiective amount of each in the inhibitor combination will be employed.

To illustrate further the present invention, some oil compositions were subjected to the L-4-545 test of the Co-ordinating Research Council, which test employs a Chevrolet engine nun for 36 hours at a jacket temperature of 200 F. and a sump temperature of 280 F. The bearings are weighed before and after the test and the average bearing weight loss is recorded as the corrosion. A weight loss of below 50 mgs. is considered excellent, a loss below 300 mgs. is considered satisfactory, but a loss above about 350 mgs. is not ordinarily satisfactory. The results obtained in this so-called L-4 Chevrolet test are given in Table VI below. The same base oil was used in all tests and the pinene-P S reaction product was the same as used in the corrosion tests set forth hereinabove. Also given forcomparison are some piston ratings obtained in tests of the oils as crankcase lubricants in a Chevrolet 6'cylinder engine operated using a low grade gasoline especially prone to cause engine deposits, the conditions being those defined in the standard FL-2 test procedure as described in the June 21, 1948, report of the Co-ordinating Research Council. This procedure requires the maintenance of a jacket temperature of 95 F. and a crankcase oil temperature of 155 F. at 2500 r.p.m. and 45 brake horsepower for 40 hours. At the end of the test, the engine is dismantled and the amount of engine deposits on the piston is determined and expressed as the i6 average piston rating. This value is obtained by visually rating (on a scale of 0 to 10, with 10 representing the absence of any deposit) the amount of deposit on each piston skirt and averaging the individual ratings so ob tained for the various pistons.

The above tests show that the inhibitor combination is also very effective in inhibiting the corrosion of bearing metals under the conditions of use as a gasoline engine crankcase lubricant. For comparative purposes, a bearing weight loss of about 250 mg. was obtained for a highly satisfactory commercial crankcase lubricant containing a calcium petroleum sulfonate, a sulfurized calcium cetyl phenate and a zinc dicetylphenyl thiophosphate.

From the above detailed description it will be apparent that the combinations of ingredients herein disclosed give a new composition having new and highly useful properties. It is immaterial for the purpose of the present invention whether the components be separately new or old, since it is the discovery of the combination of ingredients and the unexpected properties obtained thereby which comprise the applicants contribution to the art.

The compounded oils of this invention may be utilized as turbine oils, cable oils, electric switch oils, transformer oils, hydraulic oils and the like as well as in crankcase lubricants for internal combustion engines including spark-ignition and diesel engines. The compounding agents of this invention can also be added to hydrocarbon and other oils of lubricating viscosity containing additional ingredients, such as metal salt detergents (e.g., polyvalent metal phenates, phenate sulfides, sulfonates, thiophosphates, etc.), pour point depressants, oiliness agents, extreme pressure addition agents, anti-oxidants, blooming agents, compounds for enhancing the viscosity index of the oil, thickening agents and/or metal soaps in grease-forming proportions or in amounts insufficient to form grease, as in the case of mineral castor machine oils or other compounded liquid lubricants. For some purposes, for example, such as to minimize the formation of deposits tending to cause pre-ignition as sometimes occurs in aviation engines, it is desirable to avoid metal-containing compounds, and for this purpose only those additional ingredients of non-metallic character are employed.

I claim:

1. A lubricating oil composition of relatively low corrosivity to sensitive bearing metals, comprising a major proportion of a lubricating oil containing from 5 to 10% by weight of sorbitan monooleate, which ester-containing oil has high detergency but is normally corrosive at elevated temperatures to sensitive bearing metals, together with about 1 /2% to about 3% of a terpene-P S reaction product about 0.03% to about 0.5% of catechol.

2. A lubricating oil composition of relatively low corrosivity to sensitive bearing metals, comprising a major proportion of a lubricating oil containing from 5 to 10% by weight of sorbitan monooleate, which ester-containing oil is normally corrosive at elevated temperatures to sensitive bearing metals, together with about 1 /2% to about 11 3% of an oil-soluble terpene-P S reaction product and about 0.03% to about 0.5% of alizarin.

3. A lubricating oil composition of relatively loW corrosivity tosensitive bearing metals, comprising a major proportion of a lubricating oil, containing from 5 to by weight of pentaerythritol monooleate, which ester-containing oil is normally corrosive at elevated temperatures to sensitive bearing metals, together with about 1 /2% to about 3% of a terpene-P S reaction product and about 0.03% to about 0.5% of catechol.

4. A lubricating oil composition of relatively low corrosivity to sensitive bearing metals, comprising a major proportion of a lubricating oil containing aboutS to 10% by weight of pentaerythritol monooleate, which estercontaining oil is normally-corrosive at elevated temperatures to sensitive bearing metals, together with about l' /2% to about 3% of an oil-soluble terpene-P S reaction product and about 0.03% to about 0.5% of alizarin.

5. A lubricating oil composition of relatively low corrosivity to sensitive bearing metals, comprising a major proportion of a lubricating oil containing from 5 to 10% by weight of a monoester of a polyhydroxy aliphatic alcohol having four to six hydroxyl groups, the acid radical in said monoester being that of an aliphatic carboxylic acid with an oil-solubilizing chain of at least 8 carbon atoms which contains a single olefinic carbon-to-carbon double bond, together with about 1 /2% to about 3% of an oil-soluble terpene-P S reaction product and a small amount, greater than 0.03% and up to 1.5% within the limits of solubility, of an, unsubstituted vicinal dihydroxyv aryl compound selected from the group consisting of dihydroxy benzenes and dihydroxy anthraquinones.

6. A lubricating oil composition of relatively low cor hydroxyl groups with an aliphatic carboxylic acid having an oil-solubilizing chain of at least 8 carbon atoms, together with about 1 /2% to about 3% of an oil-soluble sulfurized olefin inhibitor obtained as a reaction product of an oil-solubilizing olefin and one of the class consisting of elemental sulfur and a phosphorus sulfide, and a small amount, greater than 0.03% and up to 1.5 within the limits of solubility, of a polyhydroxyl aryl compound having benzene ring substituents consisting essentially of hydroxyl groups, at least two of which are vicinal, said aryl compound being selected from the group consisting of polyhydroxy benzenes and polyhydroxy anthraquinones.

References Cited in the file of this patent UNITED STATES PATENTS 2,264,896 Bahlke Dec. 2, 1941 2,350,489 Beare June 6, 1944 2,412,633 Schwartz Dec. 17, 1946 

5. A LUBRICATING OIL COMPOSITION OF RELATIVELY LOW CORROSIVITY TO SENSITIVE BEARING METALS, COMPRISING A MAJOR PROPORTIONS OF A LUBRICATING OIL CONTAINING FROM 5 TO 10% BY WEIGHT OF AMONESTER OF A POLYHYDROXY ALIPHATIC ALCOHOL HAVING FOUR TO SIX HYDROXYL GROUPS, THE ACID RADICAL IN SAID MONOESTER BEING THAT OF AN ALIPHATIC CARBOXYLIC ACID WITH AN OIL-SOLUBILIZING CHAIN OF AT LEAST 8 CARBON ATOMS WHICH CONTAINS A SINGLE OLEFINIC CARBON-TO-CARBON DOUBLE BOND, TOGETHER WITH ABOUT 1 1/2% TO ABOUT 3% OF AN OIL-SOLUBLE TERPENE-P2S5 REACTION PRODUCT AND A SMALL AMOUNT, GREATER THAN 0.03% AND UP TO 1.5% WITHIN THE LIMITS OF SOLUBILITY, OF AN UNSUBSTITUTED VICINAL DIHYDROXY ARYL COMPOUND SELECTED FROM THE GROUP CONSISTING OF DIHYDROXY BENZENES AND DIHYDROXY ANTHRAQUINONES. 